Multibeam backscatter imagery extracted from gridded bathymetry of Rose Island, American Samoa, South Pacific
These data provide coverage between 20 and 5000 meters. The backscatter dataset includes data collected using Simrad EM300 and
Reson 8101 multibeam sonars. The sonars frequencies are 30 kHz and 240 kHz respectively and the backscatter data from each sonar
are processed and gridded separately. These metadata are for the 1 m grid cell size Reson 8101 multibeam backscatter data only.

Planar coordinates are encoded using Row and Column
Abscissae (x-coordinates) are specified to the nearest 1
Ordinates (y-coordinates) are specified to the nearest 1
Planar coordinates are specified in meters

The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257224.

Sidescan data within a GSF file are arranged as small sequences of intensity
values, one sequence per beam per ping. The intensity values represent the
amplitude of echo returns to the sensor and can be related to seabed
roughness.

The GeoTIFFs of backscatter imagery were created using data gathered from multibeam
soundings for use as a planning and reference document. The data are also being used
for benthic habitat mapping, for locating Essential Fish Habitat, and for studying
geologic features of the area. Refer to supplemental information for description of
instrument and survey.

Science Applications International Corporation's (SAIC) ISS-2000 acquires,
processes and records data, provides survey control and underway quality
control displays. SAIC's SABER processing software is used to process the
raw soundings, analyze the results, manually edit the sounding data to remove
outliers and derive average gridded data values. Additional data acquisition
and processing information can be found in the metadata for cruise AHI0602.
Hawaii Mapping Research Group (HMRG) processing software was then used to
extract values of acoustic intensity from the soundings. HMRG is an organization
of scientists, engineers and technicians whose mission is to design, build,
and operate tools for mapping the seafloor. HMRG is a group within the School
of Ocean and Earth Science and Technology at the University of Hawaii at Manoa.
The gsf2bs program (July, 2005) converts the swath bathymetry ping records contained
within a GSF (Generic Sensor Format) version 2.02 dataset into bs file format. This
is done as follows: (i) position each beam's bottom detect intensity sample at the
across-track location of that beam's bathymetry value; (ii) assuming a flat bottom
in the near neighborhood of the beam, compute across-track distances for all of the
beam's remaining intensity samples based on their temporal relation to the bottom
detect sample and the computed average sound velocity for that beam as derived from
its range and travel time; (iii) after all of the intensity samples from all beams
of a ping have been located in across-track distance, fill the gaps between them as
necessary by comparing travel times of beams adjacent to the gap, assigning the position
using the adjacent sample closest to nadir, and averaging the interpolated values that
fall within a cell. The conversion described above is necessary in order to run HMRG
backscatter processing operations on the data, such as filtering to remove noise, and to
create netCDF grids, raster images and GeoTIFF's.
For more information on the backscatter processing technique see
<http://www.soest.hawaii.edu/pibhmc/pibhmc_documentation.htm>.
Software_Used:
SAIC ISS-2000 Acquisition Software, v 3.4
SAIC SABER Processing Software, v 3.3.15
Hawaii Mapping Research Group (HMRG) Processing Software
GMT Generic Mapping Tools, v 4.1
MB System, v 5.0.7

Data are collected for resource management
and research purposes and are tested for internal consistency; however,
no effort is made to compare these data to external references or to
other published data.

These data are not to be used for navigation purposes.
Please acknowledge NOAA and the Joint Institute for Marine and Atmospheric Research (JIMAR)
University of Hawaii as the sources of this information.

These data are not to be used for navigational purposes.
NOAA makes no warranty regarding these data, expressed or implied, nor
does the fact of distribution constitute such a warranty. NOAA cannot
assume liability for any damages caused by any errors or omissions in
these data, nor as a result of the failure of these data to function
on a particular system.

TIFF is a format for storage, transfer, display, and printing of raster images. The TIFF file
structure allows both the tag and the image data to be encoded into the same file. GeoTIFF
refers to a TIFF file that has geographic data embedded as tags within the TIFF file.
The geographic data can be used to position the image in the correct location and geometry
on the screen of a geographic information display. Any GIS, CAD, Image Processing,
Desktop Mapping and other types of systems using geographic images can read any GeoTiff file.
More specifically, files of this type can be added to ArcInfo and ArcView 8.x or higher and may
be viewed in the Table of Contents as a new raster layer. Image visualization software that does
not use geography as a basis for image placement can view a GeoTIFF image as if there were no
geographic information in the TIFF file. For example, GeoTIFF files can be viewed using Windows
Picture and Fax viewer.The GeoTIFF format is public domain, non-proprietary.
in format GeoTIFF, .tif